In this project we determined the antigenic relationships based on VP4 and VP7 neutralization specificities of various rotavirus strains derived from humans and animals. The elucidation of the neutralization specificities of rotaviruses is important in order to achieve a more comprehensive understanding of rotavirus epidemiology and for formulation of an effective strategy for vaccination. By using various single gene substitution human x human or human x animal rotavirus reassortants and hyperimmune guinea pig antiserum raised against each reassortant, we determined that (i) human rotavirus strain 116E which was originally isolated from an asymptomatic infant in India carried P10 serotype specificity which is shared with bovine rotavirus strain B223, (ii) two rabbit rotaviruses (C11 and Ala) were antigenically related in a two-way fashion to human rotavirus strain PA169 and HAL1160, (iii) strain Ro1845 which was originally isolated from a child with diarrhea in Israel shared P serotype specificity with canine rotavirus CU-1 and K9 strains, (iv) murine rotavirus strains EW and EB shared the same P serotype which was distinct from established P serotypes, and (v) murine rotavirus strain EHP carried a P serotype which was distinct from all other P serotypes including that of EW and EB strains.